U.S. patent number 7,359,362 [Application Number 11/045,533] was granted by the patent office on 2008-04-15 for control of a multi-sectored antenna system to improve channel efficiency.
This patent grant is currently assigned to Microsoft Corporation. Invention is credited to James Brennan, Edward C. Giaimo, III, Wayne G. King, Chris A. Murzanski, Craig Steven Ranta, David William Russo, Stephen M. Stegner.
United States Patent |
7,359,362 |
King , et al. |
April 15, 2008 |
Control of a multi-sectored antenna system to improve channel
efficiency
Abstract
A wireless device is coupled to a multi-sector antenna that
includes a plurality of different sectors, any of which can be
activated to transmit and receive in a desired direction specific
to that sector. Optionally, an omnidirectional antenna is included
for initially establishing a wireless connection with another
wireless device, such as an access point. A parameter indicative of
signal quality, such as throughput or received signal strength
indication (RSSI) is determined by polling with each antenna sector
to establish a prioritized candidate list. If a receive Trigger
becomes active in response to a parameter falling below a threshold
level, a new candidate sector is selected from the current list
based upon a next-best signal quality. The directionality of the
multi-sector antenna provides a substantially higher data rate
compared to that of the conventional omnidirectional antenna.
Inventors: |
King; Wayne G. (Stirling,
AU), Ranta; Craig Steven (Redmond, WA), Giaimo,
III; Edward C. (Bellevue, WA), Brennan; James
(Sammamish, WA), Stegner; Stephen M. (Bothell, WA),
Russo; David William (Woodinville, WA), Murzanski; Chris
A. (Issaquah, WA) |
Assignee: |
Microsoft Corporation (Redmond,
WA)
|
Family
ID: |
36756456 |
Appl.
No.: |
11/045,533 |
Filed: |
January 28, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060171357 A1 |
Aug 3, 2006 |
|
Current U.S.
Class: |
370/338; 343/702;
370/334; 370/352; 455/418; 455/562.1 |
Current CPC
Class: |
H04W
72/046 (20130101); H04W 16/24 (20130101) |
Current International
Class: |
H04Q
7/24 (20060101) |
Field of
Search: |
;370/338,334,352
;455/562.1,418 ;343/702,709 ;342/359 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Sierra Wireless and Sprint PCS Deliver New Wireless Internet
Solution,
http://www.sierrawireless.com/news.sub.--events/news.aspx?year=2000&conte-
ntid=6A91F6A5-7193-4923-80B7-0EC323E7A60C, Aug. 23, 2000. cited by
other .
J. De Los Santos "Introduction to Microelectromechanical (MEM)
Microware Systems", Artech House, pp. 167-168 and 193, 1999. cited
by other .
Krazit, Tom "Smart Antennas to Expand Wi-Fi Range" Computerworld,
Dec. 22, 2003, Copyright 2004 Computerworld, Inc.
http://www.computerworld.com/printthis/2003/04,814,88487,00.html.
cited by other .
Office Action mailed Mar. 28, 2007, cited in related U.S. Appl. No.
11/027,748. cited by other .
Office Action mailed Jul. 18, 2007, cited in related U.S. Appl. No.
11/027,748. cited by other .
Notice of Allowance mailed Sep. 14, 2007, in related U.S. Appl. No.
11/045,687. cited by other.
|
Primary Examiner: Le; Danh
Attorney, Agent or Firm: Workman Nydegger
Claims
The invention in which an exclusive right is claimed is defined by
the following:
1. A method for conducting wireless radio frequency (RF)
communications with a wireless device using a multi-sector antenna
that is coupled to the wireless device and is able to transmit and
receive an RF signal in a desired direction, with a relatively high
gain, wherein the desired direction is selectable from a plurality
of different directions in which the antenna can transmit and
receive an RF signal, comprising the steps of: (a) associating the
wireless device in a communication link with another wireless
device; (b) determining a signal quality for RF communications with
the other wireless device using the antenna, for each of at least
some of the plurality of different directions; and (c) based upon
signal qualities determined, selecting an initial desired direction
for the antenna to be used for communicating with the other
wireless device, the initial desired direction being selected by
evaluating the signal qualities that were determined to select a
direction in which a value of the signal quality was optimum.
2. The method of claim 1, further comprising the steps of: (a)
determining a candidate list of directions for transmitting and
receiving RF signals while communicating with the other wireless
device with the antenna, based upon the signal qualities determined
for at least some of the different directions, wherein entries in
the candidate list are prioritized based upon the signal quality in
the different directions; and (b) in response to a change in the
signal quality, selecting another direction from the candidate
list, as a new desired direction for communicating with the other
wireless device.
3. The method of claim 2, wherein the step of determining the
candidate list of directions for transmitting and receiving RF
signals with the antenna comprises the step of re-determining the
signal quality for each direction of the antenna immediately before
determining the candidate list, so that a current signal quality in
each of the different directions is used in determining the
candidate list.
4. The method of claim 1, wherein the signal quality comprises at
least one of a plurality of parameters, including: (a) a data
throughput over the communication link; (b) a success in
communicating data over the communication link; (c) a received
signal strength indication (RSSI); (d) a retry count accumulated
before successfully transmitting data over the communication link;
(e) an RSSI of a returned acknowledgement (ACK) from the other
wireless device; (f) a signal-to-noise ratio; (g) an average
determined over time of at least one of the parameters (a) through
(f).
5. The method of claim 1, wherein the antenna comprises a
multi-sector antenna and each different direction corresponds to a
different sector of the multi-sector antenna, so the step of
selecting the initial desired direction for the antenna comprises
the step of selecting one of the sectors of the multi-sector
antenna for communicating with the other wireless device.
6. The method of claim 1, wherein the step of associating the
wireless device in the communication link with the other wireless
device comprises the step of using an omnidirectional antenna to
initially detect and authenticate with the other wireless device,
the wireless device communicating with the other wireless device
over the omnidirectional antenna at a relatively lower data rate
than that used for communicating with the other wireless device in
the initial desired direction using the antenna.
7. The method of claim 1, wherein the step of associating the
wireless device in the communication link with the other wireless
device comprises the step of scanning available communication
channels in at least some of the different directions until a
communication with the other wireless device is established on one
of the communication channels.
8. A memory medium having machine instructions for carrying out the
steps of claim 1.
9. A wireless station that is controllable to transmit and receive
wireless radio frequency (RF) signals in a selected desired
direction at a relatively high data rate compared to a data rate
that would be achieved if the RF signals were transmitted and
received omnidirectionally, comprising: (a) a wireless transceiver;
(b) an antenna, comprising a multi-sector antenna, that is coupled
to the wireless transceiver and is controllable to transmit and
receive RF signals in a desired direction automatically selected
from a plurality of different directions in which the antenna can
be caused to transmit and receive the RF signals; (c) a processor
that is coupled to the antenna to select the desired direction in
which it is used for communicating with the RF signals; and (d) a
memory coupled to the processor, for storing machine language
instructions, the processor executing the machine language
instructions, causing the processor to: (i) establish a
communication link with another wireless device; (ii) determine a
signal quality for RF communications conducted with the other
wireless device using the antenna, for each of at least some of the
plurality of different directions; and (iii) based upon signal
qualities determined, select an initial desired direction for the
antenna to be used for communicating with the other wireless
device, the initial desired direction being selected by evaluating
the signal qualities that were determined, to select a direction as
the initial desired direction for which a value of the signal
quality was optimum.
10. The wireless station of claim 9, wherein the machine language
instructions further cause the processor to: (a) determine a
candidate list of directions for transmitting and receiving RF
signals, while communicating with the other wireless device using
the antenna, based upon the signal qualities determined for at
least some of the different directions, wherein the directions
included on the candidate list are prioritized based upon the
signal quality determined for each direction; and (b) in response
to a change in the signal quality, select another direction from
the candidate list as a new desired direction for communicating
with the other wireless device.
11. The wireless station of claim 10, wherein the machine language
instructions further cause the processor to re-determine the signal
quality for each direction of the antenna immediately before
determining the candidate list, so that a current signal quality in
each of the different directions is used in determining the
candidate list.
12. The wireless station of claim 9, wherein the signal quality
comprises at least one of a plurality of parameters, including: (a)
a data throughput over the communication link; (b) a success in
communicating data over the communication link; (c) a received
signal strength indication (RSSI); (d) a retry count accumulated
before successfully transmitting data over the communication link;
(e) an RSSI of a returned acknowledgement (ACK) from the other
wireless device; (f) a signal-to-noise ratio; (g) an average
determined over time of at least one of the parameters (a) through
(f).
13. The wireless station of claim 9, wherein the antenna comprises
a multi-sector antenna and each different direction corresponds to
a different sector of the multi-sector antenna, and wherein the
machine language instructions cause the processor to select one of
the sectors of the multi-sector antenna for communicating with the
other wireless device, where the sector that is selected transmits
and receives in the initial desired direction determined by the
processor.
14. The wireless station of claim 9, further comprising a switch
that is coupled to an omnidirectional antenna, to the antenna, and
to the wireless transceiver, the machine language instructions
further causing the processor to active the switch so as to use the
omnidirectional antenna to initially detect and authenticate with
the other wireless device, the wireless station communicating with
the other wireless device over the omnidirectional antenna at a
relatively lower data rate than that used for communicating with
the other wireless device in the initial desired direction using
the antenna.
15. The wireless station of claim 9, wherein the machine language
instructions further cause the processor to use the wireless
transceiver and antenna to scan available communication channels in
at least some of the different directions until a communication
with the other wireless device is established on one of the
communication channels.
16. A method for controlling a direction in which radio frequency
(RF) signals are transmitted and received by a client device that
is communicating with an access point in a wireless network, the
method comprising: establishing a communication link between the
client device and the access point; determining a signal quality
associated with communication between the client device and the
access point in each of a plurality of different directions with
the use of an antenna, comprising a multi-sector antenna, that is
steerable to the plurality of different directions when
transmitting and receiving the RF signals; evaluating the signal
qualities at each of the plurality of different directions and
selecting, from the plurality of different directions, an initial
direction that provides a best signal quality for the RF signals
communicated between the client device and the access point;
enabling communication with the access point in the initial
direction by controlling the antenna to communicate RF signals in
the initial direction.
17. The method of claim 16, further comprising: steering the
antenna to each of said plurality of different directions;
detecting a value for the signal quality at each of the plurality
of different direction; and automatically prioritizing the
plurality of different directions for communication between the
client device and the access point based upon the signal quality
detected for each of the plurality of different directions.
18. The method of claim 17, further comprising the step of
responding to a deterioration of communication with the access
point in a current direction by selecting a new direction for
communication with the access point with the antenna, the new
direction being automatically selected based upon a priority of the
new direction compared to the priority of other directions.
19. The method of claim 16, wherein the step of establishing the
communication link between the client device and the access point
is carried out with RF signals conveyed by an omnidirectional
antenna.
20. The method of claim 16, wherein the signal quality comprises at
least one of a plurality of parameters, including: (a) a data
throughput when communicating with the access point; (b) a success
in communicating data between the access point and the client
device; (c) a received signal strength indication (RSSI); (d) a
retry count accumulated before successfully transmitting data
between the access point and the client device; (e) an RSSI of a
returned acknowledgement (ACK) from the access point; (f) a
signal-to-noise ratio; (g) an average determined over time of at
least one of the parameters (a) through (f).
Description
FIELD OF THE INVENTION
The present invention generally pertains to control of an antenna
used on a wireless network, and more specifically, to control of a
multi-sector antenna that is coupled to a wireless device and can
be controlled to communicate with another wireless device in a
direction selected from a plurality of different directions.
BACKGROUND OF THE INVENTION
As an increasing number of computer users install wireless networks
that meet the Institute of Electrical and Electronics Engineers
(IEEE) 802.11 specifications in their homes and workplaces, it has
become apparent that the performance (i.e., range and data rate) of
such systems often fails to meet their expectations. Structures
built of stone or brick, or which contain blocking interior
elements, such as a fireplace, mirror, refrigerator, or other large
metal or masonry furnishings, often cause problems in achieving
adequate RF coverage at a desired data throughput. Throughput can
be very important when the signal being conveyed is streaming video
or other multimedia signal that cannot be interrupted or delayed
without readily discernible adverse effects. The actual data rate
that can be achieved quickly decreases as the distance between
wireless communication devices and other factors reduce the
received signal strength of the wireless transmissions. Also, the
reception at a client device can be disrupted as a person or other
object moves through the signal path to the access point, or if the
client device, which is often a laptop or other portable computing
device, moves even a few centimeters. Wireless devices attempt to
minimize the effects of such disturbances to the signal path by
using two antennas and a diversity switch that is controlled to
automatically select the antenna providing the better signal
strength, but on a laptop wireless card, the two antennas are only
2-3 cm apart, so the benefit is not as great for more significant
disruptions in the signal path.
Existing IEEE 802.11 technologies retransmit data packets to
compensate for signal fades that cause data packets to be corrupted
or dropped during transmission. Packet retransmission is not
particularly evident to users when they perform batched operations,
such as browsing web pages. A page that loads two seconds slower or
faster on a wireless laptop, depending upon radio conditions and/or
signal strength, is typically not evident to users. In contrast,
users are cognizant and intolerant of pauses in a streaming audio
or video feed that occur while the system attempts retransmission.
Consequently, software designers of systems that use wireless links
often provide megabyte-sized jitter buffers to temporarily hold
data for retransmission/reception in an attempt to prevent
noticeable pauses or dropouts. However, these buffers cause a lag
in the media data feed (latency), increase memory requirements, and
generally make a wireless system more complex than is
necessary.
Frequently, the only way to achieve a desired coverage and
throughput in an office or home is to add more access points so
that the distance and/or intervening structural elements between
the access points and the clients devices are reduced, which means
higher wiring costs to run Ethernet cabling to the additional
access points and greater equipment costs for each added access
point. Increasing transmitter power is typically not an option due
to regulatory limitations and/or because significantly increased
power consumption is not acceptable for a battery powered side of a
link. As an alternative to adding more access points, significant
performance improvements might be achieved by providing any
existing access point and/or client device with the ability to
focus RF energy in an appropriate direction, so that the energy is
only transmitted or received in the direction required, rather than
being directed or received by one of the more conventional dual
omnidirectional antennas used on most commercially available
wireless access points and client devices.
The benefits of controlling RF energy with a directional antenna in
this manner are well known. However, the direction in which the RF
energy needs to be transmitted or received is not fixed in most
wireless systems, because a fixed access point must be able to
maintain communications with moving client devices, or communicate
with client devices that are located at different positions
scattered around the access point. A fixed directional antenna is
therefore only an acceptable solution to improve the gain of the
wireless communication signal in systems where the devices
communicating with an access point or with each other are fixed and
the link between the devices is limited to the fixed direction.
Alternatively, some commercial systems will use a plurality of
wireless transceivers, each coupled to a different directional
antenna that is directed toward a fixed wireless device. Such
systems are generally too costly for home or small business use,
however.
Electronically and mechanically steerable antennas have been used
for decades in military and industrial applications to improve the
range of radio communications links and the range of radar systems.
Unfortunately, these systems are typically large and very
expensive, and consequently, have generally not appeared in
consumer products. More recently, electronically steerable antenna
technology has been used at cellular telephone network base
stations to improve channel capacity and range. This technology is
also beginning to appear in commercial access points intended for
installation in large scale commercial applications, such as at
airports or in universities, but suitable systems still cost
thousands of dollars. A multi-sector antenna is another form of
steerable antenna and includes a plurality of sectors, each of
which can transmit and receive in a different direction, i.e.,
perpendicular to the face of the sector.
Clearly, a more affordable approach is needed that can provide most
of the benefits of these more expensive and complex systems that
have been developed for steering an antenna, but at a reasonable
cost level that is acceptable for consumer products of this type.
Such a product should control selective switching of the antenna
beam direction as needed to maintain the best communication link.
For example, a client device provided with a relatively low cost
multi-sector antenna or other steerable antenna should be able to
control the antenna to achieve a much higher data rate when
communicating with an access point, by selecting the best direction
of the steerable antenna for the communication link. The best or
preferred direction can change due to changes in the signal path,
so it would be desirable to automatically detect when any
deterioration of the signal has occurred and automatically select a
new preferred direction for the communication link.
SUMMARY OF THE INVENTION
Thus, the present invention was developed to achieve the benefits
of a directional antenna, without the problems noted above. Instead
of using a plurality of different directional antennas and a
different transceiver for each directional antenna, the present
invention selectively controls the direction used for communication
by employing a multi-sector antenna that is steerable in regard to
the direction in which it transmits and receives RF wireless
signals. This antenna is electronically steered so that a selected
sector is activated (or so that the beam of the antenna is steered
in a selected direction). The selected sector then transmits and
receives in this direction, which is defined by a phased array
antenna disposed on the sector. By selecting the sector associated
with a direction that provides the optimal signal strength or some
other criterion that is indicative of signal quality, it is
possible to achieve a much higher data rate than is possible when
transmitting or receiving in all directions at the same time (for a
given transmit power). The direction in which communications occur
can thereby be dynamically controlled to enable streaming video or
other data that requires a higher data rate to be effectively
communicated to or from the wireless device.
One aspect of the present invention is thus a method for
controlling a direction in which RF signals are transmitted and
received by a client device that is communicating with an access
point in a wireless network. The method includes the steps of
establishing a communication link between the client device and the
access point. An initial direction that provides a best signal
quality for the RF signals communicated between the client device
and the access point is then selected using an antenna that is
steerable to a plurality of different directions when transmitting
and receiving the RF signals, such as the antenna noted above.
Communication with the access point is thereby enabled in the
initial direction by controlling the antenna to communicate RF
signals in that direction.
The method preferably also includes the step of automatically
determining a signal quality associated with communicating with the
access point in each of a plurality of different directions, by
steering the antenna to the different directions and detecting a
value for the signal quality at each direction. A candidate list
for prospective directions is preferably produced by automatically
prioritizing the directions for communication with the access point
based upon the signal quality detected for each direction. This
candidate list can be created over time based upon a history
developed while communicating, or can be initially developed and
then updated, or as a further alternative, can be determined when
it appears appropriate to try communicating in a different
direction. For example, in response to a deterioration of
communication with the access point in a current direction, a new
direction for communication with the access point with the antenna
can be selected from the candidate list. The new direction will be
automatically selected based upon a priority of the new direction
compared to the priority of other directions on the list.
In one embodiment, the step of establishing the communication link
between the client device and the access point is carried out with
RF signals conveyed by an omnidirectional antenna. The
omnidirectional antenna can communicate with the access point at a
lesser range than the antenna that can be steered, and the data
rate of communication using the omnidirectional antenna will be
substantially lower than that achieved with the antenna that can be
steered to communicate in an optimal direction.
The signal quality that is used to determine the optimal direction
or to order the directions on the candidate list can comprise at
least one of a plurality of parameters. These parameters include a
data throughput when communicating with the access point, a success
in communicating data between the access point and the client
device, a received signal strength indication (RSSI), a retry count
accumulated before successfully transmitting data between the
access point and the client device, an RSSI of a returned
acknowledgement (ACK) from the access point, or a signal-to-noise
ratio. As a further option, the signal quality can comprise an
average determined over time of at least one of these
parameters.
Another aspect of the present invention is directed to a wireless
station that is controllable to transmit and receive wireless RF
signals in a selected desired direction at a relatively high data
rate compared to a data rate that would be achieved if the RF
signals were transmitted and received omnidirectionally. The
wireless station includes a wireless transceiver that is coupled to
an antenna. The antenna is controllable to transmit and receive RF
signals in a desired direction automatically selected from a
plurality of different directions. A processor is coupled to the
antenna to select the desired direction in which it is used for
communicating with the RF signals, and a memory is coupled to the
processor, for storing machine language instructions. The processor
executes the machine language instructions, causing the processor
to carry out functions that are generally consistent with the steps
of the method discussed above.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
The foregoing aspects and many of the attendant advantages of this
invention will become more readily appreciated as the same becomes
better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
FIG. 1A (Prior Art) is a schematic block diagram of a client
wireless device for communicating in an IEEE 802.11 wireless
network, which is suitable for use in connection with the present
invention;
FIG. 1B (Prior Art) is a schematic block diagram illustrating
wireless communication between an access point and a laptop client
(or other electronic device), illustrating how wireless RF signals
can be adversely affected by intervening objects that alter the RF
wireless data signal path;
FIG. 2 is an isometric view of an exemplary multi-sector antenna
for use in connection with the present invention, showing a
theoretical beam pattern for one of the sectors;
FIG. 3 is a functional block diagram of the electronic components
for one panel or sector of the multi-sector antenna of FIG. 2 (also
including a block for an omnidirectional antenna);
FIG. 4 is a composite empirically measured signal strength pattern
for all nine beams of the multi-sector antenna of FIG. 2 (it being
understood that only one beam at a time is active in normal use of
this antenna);
FIG. 5 is a functional block diagram of a wireless device that is
usable with the multi-sector antenna (and an omnidirectional
antenna) in connection with the present invention;
FIG. 6 is a software context diagram of the present invention;
FIG. 7 is a functional block diagram illustrating the use of a
vendor API and callback functions for controlling the multi-sector
antenna;
FIG. 8 is a state diagram for the present invention that
illustrates its conformance to IEEE 802.11 standards with respect
to scanning and association procedures;
FIG. 9 is a state diagram illustrating the operation of the present
invention once the multi-sector antenna is connected in
communication with another wireless device;
FIGS. 10A and 10B are flow charts respectively illustrating events
passed to the sectored antenna application in the present invention
when the wireless device connects to another wireless device, and
to enable the appropriate antenna or direction to be selected, as
well as collecting data to select candidate sectors or directions
for a candidate list;
FIG. 11 is a state diagram illustrating an overview of state
transitions;
FIG. 12 is a state diagram applicable when the multi-sector antenna
is connected in communication with another wireless device;
FIG. 13 is a state diagram applicable for a candidate scan;
FIG. 14 is a state diagram for a scan state;
FIG. 15 is a schematic diagram illustrating the interaction between
hardware and software in connection with scanning in the present
invention; and
FIG. 16 is a state diagram for sector profiling.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1A (Prior Art) is a simplified functional block diagram of a
typical wireless device like that usable with the present
invention. This wireless device includes a processor 65 that is
coupled to a PC or other computing device (not shown) so that data
device can be communicated to the processor. Processor 65 is
coupled to a memory 67, which stores machine instructions for
processing the data and for carrying out other functions. A media
access control (MAC) block 69 and physical (PHY) layer functional
block 71 are disposed between processor 65 and an RE
omnidirectional antenna 73. Although a second omnidirectional
antenna is typically provided, only one is used at a time. This
conventional wireless device does not include a directional
antenna, and it is subject to the problems noted above
communicating over a wireless network. An example of one of these
problems is illustrated in FIG. 1B (Prior Art), which is discussed
below.
In FIG. 1B, one of the problems commonly experienced by prior art
wireless devices is illustrated. A simple wireless network 20
includes an access point 22 that has two omnidirectional antennas
24 and 26. This access point communicates with a laptop 28. A PC
WiFi card 32 is included in laptop 28 and has one or more internal
antennas (not shown). Laptop 28 is able to move about access point
22, but is often used while generally fixed in position, relative
to access point 22. An object 38 (such as a person) can move into
the RF path between access point 22 and PC WiFi card 32, which can
at least temporarily disrupt or at least reduce the signal strength
of an RF signal 40, which is propagating between the two. As a
result, laptop 28 will likely (at least temporarily) experience a
substantially lower data rate for wireless communications between
it and the access point. Similarly, if the person using laptop 28
moves it about, the change in position of PC WiFi card 32 over only
a few centimeters can also substantially reduce the signal strength
of the RF signal used for communication between the access point
and the laptop due to the spatially constructive and destructive RF
signal reflections from nearby objects, commonly known as
multipath.
Access point 22 includes two omnidirectional antennas 24 and 26 to
make use of diversity antenna circuitry in the access point, which
selects the antenna employed during wireless communication to
minimize loss of signal due to dropouts and interference by using
the other antenna to receive a signal if the current antenna
experiences a reduced signal quality. However, the diversity
switching circuit includes two omnidirectional antennas and does
not choose an antenna that can change a direction in which the RF
signal will be transmitted or received. Similarly, although not
shown, PC WiFi card 32 also includes two internal omnidirectional
antennas used for diversity switching. The use of an
omnidirectional antenna with a wireless transceiver means that a
substantial portion of the RF signal that is transmitted by the
selected antenna will be propagated in directions where no other
wireless devices are located, thereby wasting the energy of the
signal. Similarly, a signal is received from all directions, which
limits the distance/data rate for received RF wireless data
communications, compared to a directional antenna. Although laptop
28 could use a directional antenna aimed toward access point 22 for
improving the quality of communications with it, the signal
transmitted or received by such an antenna cannot accommodate
changes in the signal path that occur due to objects moving into
the path and cannot readily accommodate movement of the laptop (and
antenna). The prior art generally teaches that it is desirable to
use directional antennas only if the intended transmission and
reception is in the direction favored by the directional
antenna.
To address problems such as these, the present invention employs a
multi-sector (or steerable) antenna that is controllable to
transmit/receive wireless RF signals in a desired direction, which
can be selectively varied by controlling the antenna. An example of
a multi-sector antenna system 250 is illustrated in FIG. 2, which
illustrates a nine sector antenna system 250. Each sector comprises
a generally planar panel 250a-250i, and each panel includes a
phased array of antennas (details not shown) comprising patches of
microstrip conductors. Panels 250a-250i have their ends coupled
together to form a polygon with nine sides. Since the phased array
antennas on each panel are always driven with substantially the
same delay, the beam produced by each panel is always substantially
perpendicular to the outer surface or face of the panel, as
illustrated by a graphical lobe 252. In this example, the beam
width extends approximately 40.degree. in the horizontal and about
80.degree. in the vertical direction.
Although nine panels are used in this exemplary multi-sector
antenna system, it is contemplated that either fewer or more panels
could instead be used, so that the multi-sector or steerable
antenna is more generally described as comprising N different
panels, each of which is preferably configured to employ a phased
antenna array on the panel to define a beam that is directed in a
desired direction relative to the panel. Alternatively, fewer
sectors or panels can be used and the beam can be steered to a
desired direction by modifying the delay in the signal path used
for the plurality of patches comprising the phased array on each
panel. In this manner, the beam can be caused to deflect to the
left or to the right of the perpendicular to the outer surface of
the panel that is selected to be active, and the panel selection
and beam direction can be controlled by the present invention. It
is also contemplated that the beam direction can be controlled in
three dimensions, by adding vertical control of the beam to each
panel by including additional panels above and below the panels
directed in the horizontal direction or additional phased array
patches on each panel to steer the beam produced by a panel in the
vertical direction. Thus, the present invention can control both
the active panel and can optionally control the relative delay used
to drive the patches comprising each phased array to determine the
direction in which the selected sector or panel transmits and/or
receives a wireless RF signal. Further details of the circuitry for
steering a multi-sector antenna are provided in a commonly assigned
U.S. patent application Ser. No. 11/027,748, entitled
"Electronically Steerable Sector Antenna," filed on Dec. 30, 2004,
the drawings and specification of which are hereby specifically
incorporated herein by reference. Also, another commonly assigned
and related application. Ser. No. 11/045,687, entitled
"Multi-Access System And Method Using Multi-Sectored Antenna,"
(MICR0573) filed Jan. 28, 2005, should be referenced for details
related to using a multi-sectored antenna in connection with an
access point.
FIG. 3 illustrates a schematic block diagram 200 for multi-sector
antenna system 250 that shows the component used on each panel of
the multi-sector antenna. A negative bias generator 134 receives a
direct current (DC) voltage level of from about 2.7 to 5.0 volts on
a line 136 and produces a negative bias, since the circuitry
requires both positive and negative voltage level rails relative to
a zero level. The output of negative bias generator 134 is applied
to a level shifter 138 and to a decoding logic block 140, which
receives a panel selector input to determine the sector or panel
that is selected to transmit and/or receive wireless
communications. The panel selector input can optionally be an
analog DC voltage that controls a continuously steerable antenna,
or a digital input value that selects a particular discrete antenna
sector or panel as currently active, to control the direction of
the antenna beam used for transmitting and/or receiving. The output
of decoding logic 140 is applied to PIN diode drivers 142, which
drive PIN diode shunt RF switches 206, thereby determining the
sector or panel that will transmit or receive. It should be
appreciated that some types of PIN diodes may not require the
negative bias generator to achieve the desired performance, in
which case this block and its functionality can be eliminated. In
FIG. 3, a microstrip 1:N power splitter 202 is used to split the
signal to and from the radio transceiver in regard to N-1/4 wave
transformers 204. These transformers are coupled to PIN diode shunt
RF switches 206, which determine the specific one of the N
directional microstrip antenna arrays or panels on the N-sided
polygon that will be activated for transmitting or receiving the RF
signal.
Optionally (and preferably), an omni-directional antenna 210 can be
included to transmit and/or receive a signal to/from another
wireless device and can be used for any communication with another
wireless device when the substantially higher data throughput of
the multi-sector antenna is not needed. However, the
omnidirectional antenna will typically be used in the present
invention (if included) when first establishing a communication
link with another wireless device (such as an access point), by
initially connecting with the other wireless device and
authenticating so that the wireless link is formed.
The efficacy of the present invention in communicating with the
exemplary multi-sector antenna discussed above has been shown by
tests made of a prototype model, as illustrated by the transmitted
signal strengths on a polar coordinate graph 180 that is shown in
FIG. 4. This graph illustrates a plurality of different primary
lobes 182 that are spaced apart from each other by approximately
40.degree.. Although all nine primary lobes are illustrated for the
graph of this data, perhaps giving the impression that they occur
simultaneously, each of these lobes was separately measured at a
different time, when the steerable antenna system was selectively
driven to transmit only in the direction of that lobe. Also shown
are the signal strengths of secondary side lobes 184. From this
graph, it will be apparent that the multi-sector antenna system can
be controlled to selectively determine a beam direction for
transmission or reception of an RF signal, to provide a relatively
high transmission rate in the selected beam direction, which can
enable high quality communication of streaming video and other data
that require a higher data rate.
FIG. 5 is a functional block diagram of the present invention,
illustrating how a wireless device 300 (such as a client device in
a wireless network) is configured to work with multi-sector antenna
system 250. Just as in a prior art wireless device, the present
invention includes a radio transceiver and microprocessor 302 that
is coupled to a diversity switch 304 (often included in most
wireless devices conforming to the IEEE 802.11 specification).
Diversity switch 304 is only used if an optional omnidirectional
antenna 306 is employed along with multi-sector antenna system 250.
However, unlike in the prior art wireless devices, diversity switch
304 is used in the present invention for selectively connecting
radio transceiver and microprocessor 302 to either the multi-sector
antenna system or the omnidirectional antenna and not to one of two
different omnidirectional antennas. A lead 308 connects radio
transceiver and microprocessor 302 to a PC or other computing
device (not shown).
FIG. 6 is a software context diagram illustrating the relationship
between a sector antenna application 320, which is executed by the
microprocessor included within the wireless device of FIG. 5, and
other components of the system. A wireless local-area network
station (WLAN STA) device driver 322 interfaces with the sectored
antenna application through a wireless driver 324. The device
driver is also interfaced to a network stack 328 and to other
hardware components 326 of the system. In this system, as shown in
FIG. 7, the software algorithms are implemented to interface to an
application program interface (API) that includes a WLAN vendor API
332 providing vendor interface functions that are required to be
implemented in the wireless device driver and which are available
to the sectored antenna application. IEEE 802.11 events from WLAN
device driver 322 are conveyed as signals to sectored antenna
callback functions 330. The sectored antenna callback functions
provide a mechanism for the wireless driver to signal and pass
information to sectored antenna application 320.
To better understand how the present invention operates to control
multi-section antenna system 250, it will be helpful to review
several state diagrams and flowcharts shown in the drawing and
discussed below. The present invention is implemented so as to
ensure that the wireless device still adheres to the IEEE 802.11
specification with respect to scanning and association procedures.
FIG. 8 represents an overview state diagram for the wireless device
in accord with the present invention. In an "Init" state 340, the
wireless device is awaiting an enable command from the PC or other
computing device. Once this enable command is received, it changes
to an "Unconnected" state 342 in which it is not connected to
another wireless device, but is actively searching for any base
station system (BSS). In this state, the wireless device will
process management requests from a user and BSS identification
(BSSID) scan results. In the event that a required service set
identifier (SSID) is found, the wireless device will attempt to
associate and authenticate with the other wireless device using
accepted IEEE 802.11 procedures. If provided, the omnidirectional
antenna is used in this state.
In a BSSID scan state 344, the wireless device performs an active
or a passive channel scan on selected IEEE 802.11 channels. For
example, in the IEEE 802.11g specification for the U.S., there are
11 possible channels on which wireless RF communications can be
undertaken between two wireless devices. When performing a channel
scan, a client wireless device using the present invention will
send probe requests on the omnidirectional antenna and dwell for a
short scan time period awaiting a probe response on the current
channel. If a probe response is received within the short scan
time, the client device will dwell on the omnidirectional antenna
for a long scan time to collect multiple responses. Preferably, the
short scan time is approximately equal to 20 ms and the long scan
time is approximately equal to 100 ms. While the BSSID scan state
could be implemented with the multi-sector antenna if the
omnidirectional antenna is not provided, it will then be necessary
to scan all of the available channels using each sector or panel,
which will require the short scan time for each channel. The total
channel scan for all sectors could easily take more than a second,
depending upon the number of sectors included in the multi-sector
antenna. Accordingly, it is generally preferable to use the
omnidirectional antenna for this purpose, since only a single scan
of the available channels need be done with the omnidirectional
antenna. Assuming that the scan is successful in identifying a
channel and initiating communications with another wireless device
(such as an access point), the wireless device enters a connected
state 346. In this state, the wireless device is linked in
communication with the other wireless device and is enabled to
transfer data at the relatively higher data rate using the
multi-sector antenna system.
FIG. 10A is a flow chart illustrating the events required to be
passed to the sectored antenna application when the wireless device
connects to another wireless device in a wireless network, and FIG.
10B illustrates the events that are required to be passed to the
sectored antenna application software to enable the appropriate
antenna sector or direction to be selected and to collect
appropriate statistics for making a selection of candidate sectors.
In both diagrams, typical IEEE 802.11 logical state transitions and
events are shown. In FIG. 10A, when the wireless device transitions
from an Init state 370 to an unconnected state 374, a signal 372
labeled STA_INIT is called and is used to set the omnidirectional
antenna to an active state. At this time the wireless device is not
connected to another wireless device, such as an access point but
is actively searching. When the wireless device transitions from
the unconnected to a connected state 382, a signal 378 labeled
STA_CONNECTED is called to inform the Sectored antenna
Application.
FIG. 10B describes typical IEEE 802.11 events that occur while a
wireless device is in a connected state 390. A block 392 labeled
BSSID SCAN START illustrates that the wireless device has received
a request to start a BSSID scan. An event 394 labeled
STA_BSSID_SCAN_START is signaled to the sectored antenna
application. This event is called before a BSSID scan is performed
and is used to set the omnidirectional antenna active. Next, the
BSSID scan is carried out in a step 396. A block 398 labeled BSSID
SCAN COMPLETE illustrates when the BSSID scan is complete. At this
point, an event 400 labeled STA_BSSID_SCAN_COMPLETE is signaled to
the sectored antenna application and is used to select the
continuation of the sectored antenna application algorithms. The
wireless device remains in a connected state 402.
In the event that the wireless device is disconnected from an
access point or other wireless device, as indicated at a block 404,
an event 406 labeled STA_DISCONNECT is signaled to the sectored
antenna application and is used to set the omnidirectional antenna
active. The wireless device is then in an unconnected state 408
When in connected state 390, receipt of a data frame, as indicated
at a block 410, causes an event 412 to be called, which is labeled
STA_RX_CALLBACK. This event is used to update the reception
statistics for parameters such as RSSI and may be repeated for
successive frames. The wireless device remains in a connected state
414. While in connected state 390, the wireless device can also
transmit data. Thus, a transmit indication at a block 416, causes a
data frame to be sent, which further causes an event 418 labeled
STA_TX_COMPLETE_CALLBACK to be signaled to the sectored antenna
application. This event is called after the transmission of a data
packet so that the sectored antenna application is informed about
the transmission of a data packet and can either be enabled or
disabled. Further details regarding the events discussed above and
how they are used with by the sectored antenna application are
provided below in connection with FIGS. 11-14.
Downlink/Uplink Optimization Using Historical Sector Profiling
Event 412, STA_RX_CALLBACK, is used to gather received statistics,
both for the RX trigger and for choosing antenna sector or
direction candidates that can next be used for transmission or
reception of a wireless RF signal. Event 418,
STA_TX_COMPLETE_CALLBACK, is used to collect the statistics
associated to the probes to determine a list of candidate sectors
are their relative priority. All antenna sectors are probed
periodically to determine a historical profile of the sectors. For
example a preferred embodiment uses the RSSI of the ACKs from
probes that have been transmitted by successive panels or in
successive directions to determine the candidate list priority. The
RSSI of the ACK is obtained when the TX callback event is fired.
The RX call back is used to determine the trigger and validity of a
chosen candidate.
For streaming video applications, throughput or data rate is a
preferred approach for use as an RX trigger and for verifying the
antenna panel or direction candidate chosen. A good signal data
rate is important to efficiently receive such data at a relatively
high rate, as required for an optimal user experience. Preferably,
only a subset of the possible sectors or directions will be
included as candidates when selecting a sector or direction. The
time period used for maintaining a sector candidate list is
preferably an order of magnitude greater than the measurement
period that is used for throughput or data rate determination. In
an exemplary preferred embodiment, the sector candidate list is
updated at a time interval ranging from 100 ms to one second in
duration, while the throughput or data rate for the RX trigger is
updated every 10 ms.
An exemplary state machine governing the behavior of the sectored
antenna application is illustrated in FIG. 9. Once the wireless
device is connected to another wireless device in the network, the
state machine shown in this Figure changes state as indicated. When
not being used for transmission or reception, the wireless device
is in an idle state 350. Upon being connected to another wireless
device the state changes to a connected state 352. In this state, a
candidate for a candidate list can be determined based upon
statistics or parameters that are collected in the candidate scan
state, as discussed in greater detail below. Following a timeout,
the wireless device changes to a candidate scan state 354. In this
state, probes are transmitted to determine candidate sectors or
directions for the candidate list. If the wireless device becomes
disconnected from the other wireless device, it returns to idle
state 350. Once the scan using the probes for each sector is
complete, the wireless device may switch to connected state 352. If
a STA_BSSID_START event is signaled, the wireless device may change
to a BSSID scan state 356, where a BSSID scan is carried out.
Overview of State Transitions
FIG. 11 illustrates the state transitions for an idle state 350. An
event 452 (which is corresponds to signal 378 in FIG. 10A) is
called after the wireless device is connected to another wireless
device such as an access point and is used to start the sectored
antenna application algorithms. In a step 454, the sectored antenna
is set active, and the state machine advances to connected state
352.
In FIG. 12, the state transitions for connected state 352 are
illustrated. The wireless device may respond to being disconnected
from the other wireless device as indicated by an event 462 (which
corresponds to event 406 in FIG. 10B), by setting the
omnidirectional antenna active, as indicated in a block 464. The
wireless device then changes to idle state 350. Alternatively, the
wireless device may receive a data packet as indicated by an event
466 (corresponding to event 412 in FIG. 10B), causing the update of
the received statistics or parameters. These statistics or
parameters are used for updating the RX trigger, as noted in a
block 468. A decision step 470 determines if the RX trigger is
active, and if it is, as noted in a block 474, the sectored antenna
application chooses a candidate from among the subset of sectors or
directions for use in transmitting or receiving data, and returns
to a connected state 476. If the RX trigger is not active in
decision block 470, the sectored antenna application remains in
connected state 352.
While in connected state 352, the timeout event indicated in a
block 478 may occur so that the candidate list can be updated. In
this case, the wireless device changes to a candidate scan state
480.
Also, at predefined intervals, the wireless device may initiate a
BSSID scan, as indicated in a block 482, causing the sectored
antenna application to set the omnidirectional antenna as active,
as noted in a block 484. The omnidirectional antenna is then used
for BSSID scan state 486.
FIG. 13 illustrates the transitions for candidate scan state 480.
Upon determining that the wireless device has been disconnected in
block 462, a block 464 sets the omnidirectional antenna active. The
wireless device then enters idle state 350. Also, when probe
transmissions have been completed in accord with event 466, the
candidate list information is updated, as noted in a block 510. The
candidate list can be updated based on a single current value for
the parameter being evaluated to select each candidate (i.e., the
RSSI of the returned ACK), or can be a running average of the
values for that parameter. The last sector or direction used will
preferably be pre-weighted to be disposed at the bottom of the
candidate list, since poor communications using that sector or
direction has been the basis for choosing a new candidate from the
list. A decision step 512 determines if the transmission of probes
on all of the prospective sectors or directions is finished, and if
so, the wireless device enters connected state 352, the candidate
list has now been updated. Otherwise, a probe is transmitted for
the next sector or direction, as indicated in a block 516. The
wireless device then remains in candidate scan state 480. Normally,
after the wireless device has been connected to in a wireless
network, blocks 482, 484, and 486 are only required for carrying
out a BSSID scan if it is likely that there is more than one access
point with which to connect in the wireless network. However, these
blocks are required when the wireless device is first connected
into a wireless network to find at least one access point with
which to connect. Block 482 provides for starting the BSSID scan
using the omnidirectional antenna, as noted in block 484. The
wireless device then changes to BSSID scan state 486. The BSSID
scan occurs in all states that look for a BSSID scan event.
The state transitions for BSSID scan state 486 are shown in FIG.
14. Event 462 is called when the wireless device has been
disconnected from the other wireless device or access point with
which it was previously connected in communication. Block 484 then
sets the omnidirectional antenna active, and the wireless device
changes to idle state 350. Event 538 is called when the BSSID scan
has been completed. The wireless device then reverts to its last
state, in a block 540.
The wireless device will attempt to optimize its reception of
downlink/uplink communications by detecting periods of bad
reception and switching the active antenna sector or direction to
an alternative sector or direction. It will be assumed that if the
currently active antenna sector experiences a period of bad
reception (or RF fade), then there may exist an alternative sector
or direction that will provide better reception of the RF wireless
signal. The candidates from which an alternative sector may be
chosen are preferably determined by collecting historical data for
those sectors or directions over time. This approach should give
the best chance of choosing a successful candidate as the new
active sector or direction to replace one that is now providing
poor reception.
The application software monitors the incoming received data and
generates RX Trigger Active and Inactive events. An RX Trigger On
event signifies poor receive performance, while an RX Trigger Off
event signifies acceptable receive performance. These Trigger
events are used to drive the antenna sector selection state
machine. When a different sector is chosen, the RX Trigger is
reset. If an RX Trigger event is again generated, a different
sector will be chosen, and this process repeats until a
satisfactory sector or direction is determined.
Bad Reception Detection and Fade Detection
Several techniques can be used to determine the state of the RX
Trigger, which is updated in the connected state in response to the
STA_RX_CALLBACK event. These techniques include: a determination of
the Trigger based on throughput; success or failure when sending
data packets (probes) to a connected wireless device (access
point); an RSSI for an ACKNOWLEDGE (ACK) signal received as a
consequence of data packets sent to the connected wireless device
(access point); changes in the ratio of the receive rate to signal
quality, where signal quality of the RSSI or signal-to-noise ratio
of the received data packet, when the transmission rate of the
other wireless device or access point is varied; and the packet
error rate (PER) when the transmission rate of the other wireless
device or access point is fixed.
In one preferred embodiment, throughput is determined over a 10 ms
or longer period. Successive measurements are preferably analyzed
to determine an RF fade rate. The specific number of measurements
used for this purpose is a function of the data load and how the
data are delivered over the wireless network. The measurements are
averaged over a window, producing a result that is compared to a
configurable threshold. The threshold is dependent upon the
expected data load and is set by the sector antenna application
software. In one preferred embodiment, the threshold is chosen to
equal approximately 50% of the expected data load. For this
embodiment, when the averaged throughput drops below this
threshold, an RX Trigger On event is generated. For example,
assuming a 6.6 Mbps data stream having a TCP/IP window size of 32
kB and using a conventional access point that is capable of 25 Mbps
peak data delivery, 32 kB of data will be created every 37.88 ms.
However, an access point is capable of consuming and transmitting
these data packets in approximately 10 ms. Accordingly, there
exists the possibility for 18 ms of dead time. To avoid
experiencing this dead time, a sample size of five was chosen for
the window of throughput samples. Empirically, this number of
samples has been shown to be satisfactory for determining RX
problems. The threshold is thus defined as 50% of the data load,
which is equal to about 3.3 Mbps for the above-noted example.
As an alternative approach to calculating the RX Trigger based upon
throughput, successive measurements in which the measurement
reported a zero value can be counted. This approach is similar to
the averaged window discussed above, but can be used in cases in
which processor time is limited. If the successive count of zeros
equals a maximum value, then RX Trigger is active. For example, if
the throughput measured in each of x consecutive attempts is equal
to 0 Mbps, the RX Trigger is set active.
Another method for selecting a candidate to be included on the
candidate list of sectors or directions for the multi-sector
antenna is based upon the success or failure of communicating when
using a sector or direction of the multi-sector antenna. This
parameter can be based upon the number of successes, where a small
data frame (typically a null-data) communication was sent with n
retries, or the number of retries before a successful communication
occurred, or the RSSI of an ACK frame, or the rate at which
communication was successful for a varying data rate, starting from
a high data rate and decreasing to a minimum data rate. In each of
these parameters, the number of retries, n, can range between 0 and
a ShortRetryLimit that is set by the IEEE 802.11 specification.
The wireless device can monitor the received rate from the other
wireless device or access point and the RSSI, to determine periods
when the other wireless device is experiencing difficulties
communicating with the wireless device. This approach is dependent
upon the transmit rate algorithm used by the other wireless device
or access point. The RSSI and/or SNR ratio is required to help
distinguish between loss of communication or drops due to RF
impairments, rather than transmission rate reductions that are
implemented in accord with the algorithms controlling the other
wireless device. For example, an access point may use its lowest
basic rate for data frames transmitted for its own purposes, which
are unrelated to the quality of the communication link. These low
rate data frames should not cause the sectored antenna application
executed by the wireless device to initiate an RX Trigger On event,
based upon a perceived reduction in data rates, because the data
rates were not cause by a need to change to a new sector or
direction. In evaluating this parameter, it will be necessary for
the application software to distinguish between a condition where
there is a low rate and a high signal strength, and a condition
where there is a low rate and a low signal strength. The ratio of
rate/RSSI is used to overcome these problems.
Antenna Sector Candidate Selection
The sector or direction candidates are used by the sectored antenna
application software selection procedure to identify an alternative
antenna sector when the RX Trigger is active. This list of
candidate sectors is ordered so that the most acceptable sector of
the antenna is disposed at the top of the list, followed by the
next most acceptable sector, and so forth. Periodically, the other
wireless device or access point will be probed, as discussed below,
using each of the sectors available on the multi-sector antenna.
These results are averaged over time using a weighted average to
produce an ordered list in a preferred embodiment of the present
invention. Short, null-data frames are periodically sent on each
antenna sector from the wireless device to the other wireless
device or access point. The frames are retried if the transmission
fails, up to a maximum number of retries. The sectors can thus be
profiled based upon their success/failure rate, or the transmission
rates of the probes, or on the RSSI of the returned ACK. If
success/failure rate is used, the sectors are ordered based upon
the number of retries that were used to probe the other wireless
device successfully. A lower number of retries will place a sector
higher in the ordered list, while a greater number of retries will
cause the sector to be placed lower in the ordered list. If
transmission rate of the probe is used to order the list, a
transmission rate service will attempt to optimize the transmission
rate on each sector of the multi-sector antenna, based on the
success/failure of the transmitted packet to reach the intended
recipient. The sectors of the antenna will be prioritized (or
ordered) based on the highest TX rate, and then by the lowest retry
count. If RSSI is used for this purpose, a weighted moving RSSI
average of the returned ACK is applied to order the sectors of the
multi-sector antenna on the list. Typically, a moving average RSSI
window size includes from five to 10 samples.
Probe Synchronization
To enable the sectored antenna application to send probes to
another wireless device or access point using the available
different antenna sectors/directions, the transmission of each
probe must be synchronized with the switching of the multi-sector
antenna to each different sector or direction. FIG. 15 illustrates
how the sectored antenna application software and the hardware of
the multi-sector antenna interact. A sector scan is requested by
the application software in a block 550, which halts the
application software queue, as indicated at 552, giving the
hardware queue time to empty. The application checks the hardware
queue length at 554 and waits until the hardware queue has emptied
of data, as noted at a block 556. In a block 558, the application
software sets a current antenna sector and sends a power save flag
to the access point (or other wireless device). The application
software then commands the hardware to send a probe to the access
point using the current sector of the multi-sector antenna, as
indicated at 560. Preferably, the probe is simply a short frame of
null data, such as the IEEE 802.11 Null-Data frame. At 562, an ACK
is received from the access point if the attempted probe
communication was successful, or if not, the wait for an ACK to be
received times out (after a predefined time interval has elapsed).
Based upon the results of the probe, the candidate list is updated.
If successful, the then current sector is added to the candidate
list, along with a parameter indicating the signal quality for that
sector. If all sectors have not yet been probed, the next sector
(or direction) of the multi-sector antenna is used for sending the
probe at 560. A loop 566 back through block 558 is repeated until
all sectors (or a desired subset) have been used for the probe. A
flag to disable the power save function is then sent with null-data
(or actual data if available to be sent) to the other wireless
device or access point in a block 568. As noted at 570, the
application software queue is then restarted and communication
proceeds with the top candidate on the candidate list (which has
been ordered according to the signal quality for each of the
sectors for which the probe was successful).
To minimize the time spent dwelling on each antenna sector, the
probes will be queued as if there were high priority data packets
to be transmitted by the wireless device. The transmit engine of
the radio transceiver used in the wireless device will then
transmit these null data packets used for the probes with a lower
than normal contention window (CW) parameter (a procedure defined
by the IEEE 802.11e specification).
Downlink/Uplink Optimizing Using Immediate Sector Profiling
In this alternative approach, the candidate list is maintained in a
substantially different manner. When the RX Trigger becomes active,
the other wireless device or access point is immediately probed
using all antenna sectors. Based upon the results of these probes,
a candidate is chosen. FIG. 16 illustrates a state diagram showing
the changes necessary to perform immediate sector profiling in this
manner. The immediate sector profiling uses the RSSI of probes that
are sent on each of the antenna sectors. When it is necessary to
use a different sector, all sectors are immediately poled to create
a current candidate list based on current averages of a parameter,
rather than using a historically developed candidate list that was
determined over time.
Referring to FIG. 16, a connected state 580 can change to a probing
state 582 if the RX Trigger becomes active. When the RX Trigger On
event becomes active, a power save flag is sent to the other
wireless device, transmissions are halted, a probe timeout elapses,
and probing begins. In probing state 582, the wireless device sends
null-data using each sector of the multi-sector antenna. At each
time out, the application software changes to another sector and
sends another frame of null-data. Parameters such as
success/failure, rate, and RSSI are updated for the current sector.
After all sectors have been probed, the candidate list is checked,
and if the list contains a better sector than the current sector, a
change is made to the best candidate sector, and the RX Trigger is
reset. Based upon these immediate results, a new candidate 584 is
thus chosen. However, if the candidate list is empty after all
probes have been sent, the RX Trigger is reset, and reception
continues using the original sector.
Signal quality, whether determined historically over time, or
immediately when selecting a new sector, can be based on one or
more of a number of different parameters. These parameters include
a data throughput over the communication link; a success in
communicating data over the communication link; a received signal
strength indication (RSSI); a retry count accumulated before
successfully transmitting data over the communication link; an RSSI
of a returned acknowledgement (ACK) from the other wireless device;
or a signal-to-noise ratio. It is also contemplated that a running
average determined over time of at least one of these parameters
can be used to assess signal quality.
Although the present invention has been described in connection
with the preferred form of practicing it, those of ordinary skill
in the art will understand that many modifications can be made
thereto within the scope of the claims that follow. Accordingly, it
is not intended that the scope of the invention in any way be
limited by the above description, but instead be determined
entirely by reference to the claims that follow.
* * * * *
References